1. Field of the Invention
This invention relates to a technique of hot pressing boards in wood working.
Throughout the specification, by the term "board" are meant wooden boards such as laminated wooden boards, aggregated boards, fiber boards, wafer boards, and particle boards, and also laminate boards made of such plants as kaoliang, and by the term "hot pressing" is meant a process of pressing the work while heating the same.
2. Description of the Prior Art
FIGS. 25 to 27 show a well-known technique for hot pressing boards. As shown in FIGS. 25 and 26, a board 12 as a work is put on a caul plate 20, which is then conveyed by a conveying mechanism 40, for instance, a pusher, to a hot pressing section 31.
The caul plate 20 is moved horizontally as it is conveyed by the conveying mechanism 40, and is set in a predetermined hot pressing position in a hot pressing section 31. Above the hot pressing section 31, a hot pressing mechanism 30 is disposed, which is constituted by a hot plate 32 and a spacer 33.
As shown in FIGS. 26 and 27, in the hot pressing section 31, the board 12 put on the caul plate 20 is pressed by the hot plate 32 of the hot pressing mechanism 30. The hot plate 32 has been preliminarily heated, and the board 12 can receive heat therefrom and is thus hot pressed.
As for the extent of pressing the board 12 to obtain a given thickness thereof, with the pressing of the board 12, the spacer 33 which is configured to project from the hot plate 32, is brought into contact with the caul plate 20, and thus serves as stopper to determine the extent of pressing.
As shown in FIG. 27, a hot pressing region in which the board 12 is pressed, is a closed space 36 defined by the hot plate 32, the spacer 33 and the caul plate 20.
The spacer 33 has steam supply ports 35 formed therethrough. While the board 12 is pressed, steam is supplied to the closed space 36 through the steam supply ports 35 for perfect hot pressing of the board 12. The steam supplied can maintain a high pressure in the closed space 36, and therefore can be readily impregnated into the board 12.
In the above prior art technique of hot pressing boards, however, the board 12 put on the caul plate 20 is conveyed to the hot pressing section 31 by the conveying mechanism 40, and the caul plate 20 is moved horizontally as it is conveyed by the conveying mechanism 40 to be set in a hot pressing position. This means that the caul plate 20 may be in frictional contact with other members to result in its wear or deformation. In addition, various parts or members constituting the hot pressing section 31, with which the caul plate 20 is in frictional contact, may be worn out or deformed.
The wear or deformation of the caul plate 20 and various parts or members constituting the hot pressing section 31, disables formation of the closed space 36 by the hot plate 32, spacer 33 and caul plate 20 when hot pressing the board 12. In other words, the wear or deformation results in the formation of a clearance between the caul plate 20 and the spacer 33, and heat or steam supplied at the time of hot pressing may leak out through the clearance.
Such leakage of heat or steam reduces the temperature or steam pressure in the closed space 36, thus reducing the efficiency of hot pressing.